1. Field of the Invention
This invention relates to a vertical pearling machine for pearling wheat or like grains and also to an apparatus for preliminary treatment for flour milling using a plurality of such vertical pearling machines connected in tandem.
2. Description of the Related Art
In a broadly practiced method of producing wheat flour, the raw wheat which has been cleaned and conditioned is directly broken without its bran part being removed, and its endosperm part (about 84% by weight) which is to be eventual product flour is separated from its bran part (13.5% by weight) and its germ part (2.5% by weight), these bran and germ parts being undesired as contents in the product flour. The introduction of the bran part which contains much ash deteriorates the quality of the product flour, and therefore the content of this part should be made as little as possible. To this end, prior to the flour milling, the row material is conditioned with water or steam and then tempered in a tempering bin for 4 to 20 hours for making each wheat grain bran layer tough and the endosperm soft.
By carrying out these preliminary treatments prior to the flour milling process, the flour milling characteristics are generally improved. Depending on the tempering time, however, the coupling between the endosperm and the inner bran layer is rather strengthened to make the separation of the endosperm and bran parts difficult. In view of this problem, a technique of removing the bran, which is undesired to be contained in the product flour, prior to the flour milling, has been proposed as disclosed in, for instance, Japanese Patent Application Kokai Publication No. Hei 2-184347. This prior art will now be described with reference to the flow chart of FIG. 1.
As shown in the Figure, the cleaned raw wheat A is first fed to a water additioner 101 for adding a slight amount of water to soften its bran. Then, it is immediately pearled in a pearling process 106, which is constituted by a tandem connection of friction units (i.e., friction type pearling machines) 102 and 103 and abrasive units (i.e., abrasive type pearling machines) 104 and 105. While the material is pearled, further water is added to moisten the material surface. The pearled wheat B thus obtained is fed through a wiper 107 and a cooler 108 to a further water additioner 109 for further water addition to obtain conditioned pearled wheat C containing about 16% of water by weight.
In the above prior art, however, since water is added to the pearled wheat obtained after the pearling process 106, the starch layer of the wheat may be dissolved to result in sticking of wheat grains to one another into masses. A large-scale stirrer, therefore, has been necessary to prevent the mutual sticking of wheat grains.
To solve this problem, it may be thought to moisten and temper the material wheat prior to the pearling thereof. By moistening, however, the wheat bran is made tough as noted above. In this condition, the pearling does not proceed sufficiently with the conventional grinding type pearling machine. In addition, since the endosperm part is softened, a large amount of breakage occurs in the friction type pearling machine.